Botez, in U.S. Pat. No. 4,215,319, incorporated herein by reference, has disclosed a constricted double heterostructure laser, composed of Group III-V compounds and alloys of such compounds, which includes a substrate having a pair of spaced, substantially parallel grooves with a mesa therebetween in a surface thereof. A first confinement layer overlies the surface of the substrate, the mesa and the surfaces of the grooves, an active layer overlies the first confinement layer and a second confinement layer overlies the active layer. The active layer tapers in increasing or decreasing thickness in the lateral direction, the direction in the plane of the layers and perpendicular to the axis of the grooves, depending upon the crystallographic orientation of the substrate surface and the surface curvature of any underlying layer. Botez, in U.S. Patent application Ser. No. 251,651 filed Apr. 6, 1981, U.S. Pat. No. 4,347,486, and incorporated herein by reference, has disclosed a constricted double heterostructure laser having a guide layer which is interposed between the first confinement layer and the active layer and which also tapers in thickness in the lateral direction. Botez et al. in U.S. Patent application Ser. No. 257,773 filed Apr. 27, 1981, U.S. Pat. No. 4,383,320, have disclosed a laser having a guide layer wherein the surface which contacts the active layer has a concave shape in the lateral direction over the mesa between the grooves and tapers in increasing thickness in the lateral direction.
In each of these lasers the deposition of the layers on the substrate surface, the grooves and the mesa is non-uniform because the layer growth is faster over concave portions than over flat or convex portions of the surface. This non-uniform growth produces the curvature of the deposited layers and the resulting taper. The degree of curvature, and thus the yield of useful devices, obtained is, however, sensitive to the thicknesses of the deposited layers and fluctuations in the growth conditions.
A change in the structure of these devices which produced an increase in the curvature of the deposited layers and increased the yield of useful devices would thus be desireable.